1. Field of the Invention
This invention pertains to a method and device for determining the polarity of a signal generated and transmitted by an animal containment system. More particularly, this invention pertains to a method and device for determining the polarity of the signal at the location of an animal.
2. Description of the Related Art
Conventional pet containment systems typically include a transmitter unit, a wire, and a receiver unit. The wire defines a perimeter such as, for example, the perimeter of a pet owner's yard. The transmitter unit is in electrical communication with the wire and transmits a signal by way of the wire such that the signal generates a magnetic field that rotates about the wire. The receiver unit is carried by a pet and is responsive to the signal transmitted by way of the wire. More specifically, when the pet approaches the wire, the signal strength at the receiver unit increases until it exceeds a predefined threshold, which occurs some distance from the wire. When the signal strength at the receiver unit exceeds the threshold, the receiver unit delivers a stimulus to the pet, discouraging the pet from leaving the pet owner's yard.
The above-discussed conventional pet containment systems are limited in that the receiver unit delivers a stimulus to the pet when the pet is some distance from the wire, which defines the perimeter of the pet owner's yard. Consequently, the pet does not have unfettered access to the entire yard. Additionally, conventional pet containment systems of this sort present confusion to a pet when visible physical boundaries, such as a fence, are located at the perimeter of the yard.
Other conventional pet containment systems address the above-discussed limitation by decreasing the strength of the signal transmitted from the wire such that the distance from the wire at which the signal strength at the receiver unit exceeds the threshold is decreased, increasing the portion of the yard to which the pet has unfettered access. However, when that distance is decreased, the risk of the pet escaping the conventional pet containment system is increased. More specifically, the distance from the wire at which the signal strength at the receiver unit exceeds the threshold must be sufficiently large such that when the pet is running toward the wire, the receiver unit delivers a stimulus to the pet for a period of time sufficient to stop the pet's advancement toward the wire before the pet traverses the wire and moves the distance beyond the wire at which the signal strength at the receiver unit does not exceed the threshold. When this distance is not sufficiently large, the pet can easily, and even accidentally, move beyond the perimeter of the yard to the extent that the receiver unit does not deliver a stimulus to the pet. Additionally, when this occurs, the pet cannot reenter the yard without the receiver unit delivering a stimulus to the pet. This confuses the pet and encourages the pet to remain outside the yard.
Addressing the above-discussed limitations of conventional animal containment systems, U.S. Pat. No. 5,794,569, issued to Titus et al. on Aug. 18, 1998, (“the '569 patent”) discloses the conventional animal containment system discussed above where the receiver unit is adapted to detect the polarity of the signal transmitted by way of the wire. Because the transmitted signal generates a magnetic field that radiates from the wire, the signal rotates about the wire such that the polarity of the signal at one side of the wire is substantially opposite the polarity of the signal at the opposite side of the wire. Stated differently, the polarity of the signal at a location within the perimeter is substantially opposite the polarity of the signal at a location outside the perimeter. The system of the '569 patent detects the polarity of the signal at the location of the receiver unit by transmitting an independent polarity pulse as part of the signal transmitted by way of the wire. The polarity pulse serves no purpose but to indicate to the receiver unit the polarity of the signal at the receiver unit. The receiver unit of the '569 patent delivers a stimulus to the pet only when it detects that the pet is approaching the wire from within the perimeter. Consequently, when the pet does traverse the wire and is outside the perimeter, the pet can reenter the yard without the receiver unit delivering a stimulus to the pet. The conventional pet containment system of the '569 patent is limited in that the polarity pulse contains no information relating to operating instructions for the receiver unit. Consequently, the independent polarity pulse increases the number of transmitted pulses per signal, which increases the required power to transmit the signal and the required signal processing at the receiver unit. Consequently, a pet containment system that contains a pet within a boundary, that maximizes the pet's usable area within the boundary, that does not discourage the pet from returning to within the boundary in the event the pet moves beyond the boundary, and that does so without utilizing an independent polarity pulse is desired.